The present invention relates to a regenerative pump and more particularly to a regenerative pump which reduces pump noise.
A conventional regenerative pump will now be described with reference to FIGS. 12 to 16. FIG. 12 shows a motor-driven pump unit to suck up fuel for automobiles and the like from a fuel tank, in which a regenerative pump 200 is provided in a lower part of the pump unit. The regenerative pump 200 includes a body 204 constituting a pump wall of the lower side of the regenerative pump 200 with a fuel inlet hole 202 (see FIG. 14), a first impeller 208 and a second impeller 210 both fixed to an armature shaft 206 of a motor disposed substantially in the center of the pump unit, an annular intermediate plate 212 interposed between the first impeller 208 and the second impeller 210, and a cover 214 constituting a partition wall between the motor and the regenerative pump 200. A central hole 216 for inserting the armature shaft 206 and an outlet hole 218 shown in FIG. 16 leading to the motor are formed on the cover 214. Reference numerals 220 and 222 designate first and second annular spacers disposed concentrically surrounding the first impeller 208 and the second impeller 210 and constituting a pump wall in the radial direction. The cover 214 is caulked to the end portion of a motor casing 221, to which the second spacer 222, the intermediate plate 212, the first spacer 220 and the body 204 are piled in this order and secured by screws 214.
On the body 204, the intermediate plate 212 and the cover 214, there are provided grooves 204a, 212a and 212b on both sides of the intermediate plate 212 facing the first impeller 208 and the second impeller 210 as well as 214a at the positions corresponding to vane channels 208a and 210a formed at the outer peripheral portion of the first impeller 208 and the second impeller 210. These grooves 206a, 212a, 212b and 214a extend within the predetermined respective angles. The grooves 204a and 212a facing the outer periphery of the first impeller 208 and an inner circumferential surface of the first spacer 220 constitute a first flow passage 228 starting from the inlet hole 202 leading to a communication hole 226 shown in FIG. 15 and 16 through the intermediate plate 212. As shown in FIG. 15, at the inner circumferential surface of the first spacer 220, a partition wall 230 is formed projecting inwardly in the radial direction within the range between the inlet hole 202 and the communication hole 226 and having an arcuate surface 230a of substantially the same diameter as the first impeller 208 so as to prevent flow of the fuel therebetween.
Similarly, the grooves 214a and 212b facing the outer periphery of the second impeller 210 and an inner circumferential surface of the second spacer 222 constitute a second flow passage 232 starting from the communication hole 226 leading to the outlet hole 218. As shown in FIG. 16, at the inner circumferential surface of the second spacer 222, a partition wall 234 is formed projecting inwardly in the radial direction within the range between the communication hole 226 and the outlet hole 218 and having an arcuate surface 234a of substantially the same diameter as the second impeller 210 so as to prevent the flow of the fuel therebetween. Reference numerals 236 in FIG. 15 and 238 in FIG. 16 show insertion holes formed through the first spacer 220 and the second spacer 222 for inserting screws 224 thereinto.
This kind of motor-driven fuel pump is arranged to conduct electricity to the motor through a connecting terminal 240 and rotate the armature shaft 206, thereby rotating the first impeller 208 and the second impeller 210 and sucking up the fuel in the fuel tank (not shown) from the inlet hole 202 and pumping the same from the first flow passage 228 through the communication hole 226 to the second flow passage 232 and further to within the motor casing 221 through the outlet hole 218 and then to the outside of the pump unit through an outlet port 242 after passing around the armature.
In the regenerative pump 200 described above, when the fuel flows from the first flow passage 228 to the communication hole 226 and from the second flow passage 232 to the outlet hole 218, the fuel strikes against one end of the corresponding partition walls 230 and 234 in the state of a spiral vortex (the spiral vortex like this as shown by an arrow in FIG. 13 flows outwardly in the radial direction along the vane channels 208a, and strikes against the wall in the radial direction of the flow passage 228, and flows inwardly in the radial direction along the grooves 204a and 212a and then flows outwardly in the radial direction again along the vane channels 208a, which is a circulated flow.), causing a high-frequency sound with a frequency of the number of vanes of the first impeller 208 and the second impeller 210 multiplied by the number of rotation of the impellers per second, resulting in a noise (so called impeller noise).
Japanese Patent Publication Nos. 39-9738 and 39-13692, Japanese Utility Model Publication Nos. 39-143, 46-8745 and 47-21203 and Japanese Utility Model Laid-Open Publication No. 52-126303 propose structures to change the configuration of the flow passage at the outlet side in various ways so as to reduce the noise. Japanese Patent Publication No. 39-13692, for example, discloses the structure of gradually decreasing the cross-sectional area of the flow passage.
Japanese Patent Laid-Open Publication No. 58-101263 discloses the structure providing in the flow passage at the region of the outlet side with a straight portion substantially extending in the tangent direction from an impeller. The straight portion extends to the outside of the regenerative pump and is connected to an outlet pipe rising up in the axial direction of the motor body and disposed on the outside of the motor housing. This structure may reduce an impeller noise, however, the outlet pipe is provided outside the pump unit. Therefore, the size of the pump becomes large and the motor is not cooled by the flow of fluid. Moreover, it is difficult to adopt this structure for multi-stage regenerative pump.